The present invention relates generally to tube cutters and, more particularly, is directed to an improved tube cutter for cutting off a tube section having a circumferential bulge, such as, a composite tube section formed by two concentric tubes which have been mechanically joined together by circumferential bulging as is a common practice in the nuclear reactor industry in constructing a basic fuel assembly structure.
As shown in U.S. Pat. No. 3,791,466, the basic fuel assembly structure for a nuclear reactor comprises a skeleton assembly made up of longitudinally extending hollow tubes or thimbles composed of zirconium base alloy, such as Zircaloy, and held in place by Inconel or stainless steel transversely extending grids disposed between stainless steel end nozzles at the top and bottom of the structure. The tubes serve as guide thimbles for cylindrical control elements strategically located in a square array of fuel rods held in place by spring fingers on the "egg-crate" grids. The guide thimbles are attached to the top and bottom nozzles and the grids are axially spaced along the guide thimbles and mechanically attached thereto by bulge expanding a sleeve, which is welded to the grid, onto the guide thimble.
By virtue of their zircalloy strap design, these grid assemblies contain inherently high material costs and therefore it is economically desirable to salvage them rather than to let them become nonfunctional scrap. However, due to the specific design and construction of these assemblies, salvage is constrained by several problems, namely: the grids are permanently affixed to the skeleton structural (thimble) tubes by mechanical bulges (deformations) between the sleeves, which are welded to the grids, and the thimbles; the bulges are located very close to the grid strap plane, which is perpendicular to the assembly axis and limits normal access; clearances are severely limited by thimble-to-thimble centerline spacings which are typically less than three-fourth inch between neighboring thimble outside diameter surfaces; and the grids must be protected from vibration, shock, and other forces which could have a deleterious effect on their structural integrity.
There are several tube cut-off tools on the market, such as the ones identified in U.S. Pat. Nos. 554,028; 1,857,493; 2,448,578; 2,571,916; 2,937,440; 2,983,043; and 3,608,194; however, none of these prior art cutters, for one reason or another, are capable of performing the tube cutting needs as set forth above. Thus, the need exists for a new tube cutter for cutting a tube section formed by a pair of concentric tubes joined together by a mechanical bulge wherein diametrical clearances and access are severely limited.